Authorship：Lead author   Publishing type：Research paper (scientific journal)  

© 2018 the Owner Societies. Femtosecond excited-state dynamics of fullerene-C60 nanoparticles (nC60) having a mean size of 50 nm dispersed in pure water was studied by means of femtosecond transient absorption spectroscopy. The intermolecular charge-transfer (CT) excited state in solid C60 was directly and firstly observed by femtosecond 350 nm and 420 nm excitations, and its intrinsic lifetime of 0.35 ps was found. The CT excited state relaxed to the locally excited S1 state and excimers or directly to the ground state through geminate charge recombination. We also examined the laser fluence dependence of the CT excited-state dynamics. At a high laser fluence, the mutual interactions between neighboring CT excited states were observed immediately after the excitation. The interaction disappeared through the charge recombination in the geminate CT pair or between the neighboring CT excited states with a lifetime of 0.45 ps. After that, the locally excited S1 state decayed with a few ps lifetime independent of the fluence. In this paper, the mechanism and dynamics of the intermolecular CT excited state generated by UV light excitation is discussed in detail.

DOI： 10.1039/c7cp06746a

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We have investigated the excitation intensity dependence of the singlet fission in a crystalline rubrene by means of femtosecond transient absorption microspectroscopy. When a rubrene microcrystal was excited to higher energy levels than that of the lowest singlet excited (S-1) state with a 397 nm femtosecond laser pulse, a triplet excited state was formed through two pathways of the singlet fission, i.e. the direct fission from higher vibrational levels of the S-1 state with a time constant of 2.2 ps and the thermally activated fission from the S-1 state in a few tens of ps. The time constant of the thermally activated fission changed from 35 to 17 ps for increasing of the laser fluence from 0.65 to 18 mJ cm(-2) per pulse, although that of the direct fission was constant with the excitation laser intensity. On the other hand, the yield of the triplet formation was independent of the intensity. We also examined the temperature dependence of the singlet fission and demonstrated the activation energy of the thermally activated fission to be 0.21 eV. Based on the experimental results, we considered the excitation intensity dependence of the singlet fission of the rubrene crystal in terms of the effect of transient local heating on a ps time scale after femtosecond laser excitation owing to the nonradiative vibrational relaxation from the higher vibrational level to the lower one in the S-1 state.

DOI： 10.1039/c6pp00171h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have developed a femtosecond pump probe light scattering microspectroscopic system in which the output of a femtosecond Ti:sapphire oscillator (1 W, 82 MHz) was used as a light source; the pump light is the second harmonics (395 nm) of the laser output, and the probe light is a femtosecond white-light continuum (490-900 nm) generated with a photonic crystal fiber. Detection of the backscattered light from single nanoparticle on a glass substrate allowed us to obtain higher gain of the transient signals by similar to 20 times in comparison with the conventional transmittance-mode experiment. This high-sensitivity of the back scattering detection makes it possible to examine ultrafast relaxation dynamics of excited states in organic nanoparticles, which, in general, are lower photodurability than the inorganic one. We applied the system to single nanocrystals of a-form perylene and then succeeded in direct observation of the excimer formation dynamics on a picosecond time scale. Single nanoparticle measurements for the perylene nanocrystals having a size range of 100 to 500 nm suggested that the excimer formation time became short from 2 ps to <0.3 ps for decreasing of the size.

DOI： 10.1021/acs.jpclett.6b01330

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Independently stacked positively and negatively charged π-electronic systems in charge-segregated columnar structures are desired for electronic properties derived from their electron-deficient and -rich assembling states, respectively. An expanded π-electronic cation, benzoporphyrin...

DOI： 10.1039/d4sc07576e

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DOI： 10.1021/acs.jpcc.4c07079

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DOI： 10.1007/s10854-024-12542-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Optical fibers of a typical chalcogenide glass, As₂S₃, can be sharply bent only by sideward irradiation of polarized light. The bending direction depends on the polarization; the fiber bends in the forward/backward directions of light propagation for bandgap light that is linearly-polarized orthogonal/parallel to the fiber axis. A reciprocity law between the intensity and the exposure time holds, which suggests that thermal effects are irrelevant. Alternatively, the bending appears to arise from photo-induced optomechanical forces and fluidity. This phenomenon could be developed to a photo-manipulation method of chalcogenide-glass fibers, promising for all-optical switching/modulation devices working at infrared wavelengths.

DOI： 10.35848/1882-0786/ad09ee

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Other Link： https://iopscience.iop.org/article/10.35848/1882-0786/ad09ee/pdf

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Squarylium-based π-electronic cation with an augmented dipole was synthesized by methylation of zwitterionic squarylium. The cation formed various ion pairs in combination with anions, and the ion pairs exhibited distinct photophysical properties in the dispersed state, ascribed to the formation of J- and H-aggregates. The ion pairs provided solid-state assemblies based on cation stacking. It is noteworthy that complete segregation of cations and anions was observed in a pseudo-polymorph of the ion pair with pentacyanocyclopentadienide as a π-electronic anion. In the crystalline state, the ion pairs exhibited photophysical properties and electric conductivity derived from cation stacking. In particular, the charge-segregated ion-pairing assembly induces an electric conductive pathway along the stacking axis. The charge-segregated mode and fascinating properties were derived from the reduced electrostatic repulsion between adjacent π-electronic cations via dipole–dipole interactions.

DOI： 10.1002/anie.202216013

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.202216013

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The birefringence in As2S3 glass that is induced by either uniaxial stress or illumination with linearly-polarized light ((h) over bar omega = 2.0 and 2.3 eV) is comparatively studied using a specially-designed phase meter operating at a wavelength of 633 nm (similar to 2.0 eV). The photoelastic constant of As2S3 is negative (-6 x 10(-12) Pa-1): the refractive index parallel to an applied uniaxial stress becomes smaller, which is contrastive to that (+3.5 x 10(-12) Pa-1) in SiO2 glass. On the other hand, the photoinduced birefringence in As2S3 is also negative; i.e., the refractive index in the direction parallel to the electric field of excitation light becomes smaller than the perpendicular. These resembling features with comparable magnitudes of the stress- and photo-induced birefringences imply common structural origin. We propose that the negative birefringences can be understood by a unified model that assumes anisotropically-aligned segmental layer structures which are produced by mechanical and photo-structural atomic motions.

DOI： 10.1016/j.jnoncrysol.2022.122017

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Modifications in curved pi-electronic systems, dipyrrolylbenzodiazepines, resulted in various derivatives with modulated electronic properties and assembly behaviour. The electron-rich pyrrole-based curved pi-system exhibited C-60 complexation in the form of a hydrogen-bonding cyclic hexamer, giving rise to solid-state photo-induced electron transfer as elucidated by transient absorption spectroscopy.

DOI： 10.1039/d2cp01575g

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In this study, charged π-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces.iπ-iπ Interaction, defined herein, functions for the stacking structures consisting of charged π-electronic species and is in contrast to conventional π-π interaction, which mainly exhibits dispersion force, for electronically neutral π-electronic species. Establishing the concept ofiπ-iπ interaction requires the evaluation of interionic interactions for π-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing π-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species,viaNa+in the intermediate ion pairs, for synthesized π-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA+) and π-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA+) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of π-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the π-electronic anion in the charge-segregated mode.

DOI： 10.1039/d1sc02260a

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A novel femtosecond pump-probe microspectroscope using a femtosecond Ti:Sapphire oscillator as a light source was developed. The fundamental specifications are the temporal resolution of 350 fs, the spatial resolution of 770 nm, and the tunable probe wavelength in the region from 500 to 900 nm. The setup has two modes of the probe light detection; one is back-scattered light detection and another conventional transmitted light detection. The back-scattering mode measurement demonstrated about 20-times higher gain of the transient signal of single nanoparticles compared to the conventional transmittance-mode one. This high-sensitivity enables the single nanoparticle ultrafast spectroscopy of organic nanomaterials which in general are low photo-durability. The femtosecond pumpprobe microspectroscopy is fruitful in the researches of solid-state photochemical processes characterized by restricted molecular motions and intermolecular electronic interactions in the confined space. The potential applications of the developed microspectroscopic system are demonstrated for the picosecond excited state dynamics of nm- to μm-sized organic crystals.

DOI： 10.1007/978-981-15-5451-3_29

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© 2019 The Japan Society of Applied Physics. One- and two-photon absorption coefficients in Bi2O3-B2O3 and Bi2O3-SiO2 glasses, which are characterized with zero photoelasticity and visible transparency, are studied. The two systems show a similar compositional dependence in photoelastic constant (PEC), which can be accounted for by electronic structure of Bi3+. The one-photon absorption coefficients in borate and silicate glasses depend on the existence of charge transfer phenomena, while the two-photon absorption coefficients obtained by Z-scan measurement is independent of the one-photon absorption. The interpretation by optical transition probabilities can be extended to elucidate the optical nonlinearity in ns2-type cation containing oxide glasses with zero PEC.

DOI： 10.7567/1882-0786/ab40f4

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

Supramolecular assemblies have been extensively studied because of their fundamental insights into intermolecular interactions and their potential applications to optoelectronic devices. Among various molecular building units, 2,4,5-triphenylimidazole (lophine) has been extensively studied because the molecule itself gives chemiluminescence and bright fluorescence and because it forms various anisotropic nanostructures. While various potential applications such as to optoelectronic and lasing devices have been reported in lophine-based nanostructures, the relationship among molecular structures, nanostructures, and their optical properties remains elusive. This study reveals that the hydrogen bonding of the imidazole ring plays a crucial role for one-dimensional anisotropic nanostructures and their optical properties. The hydrogen bonding leads to thermodynamically stable nanofibers and gives a monomeric sharp emission, while it also induces ultrafast nonradiative relaxation. On the other hand, the π-π interaction leads to kinetically favorable nanoparticles and gives a broad emission due to the excimer of the perylene moiety. The insight into the relationship among molecular structures, nanostructures, and optical properties are important for on-demand optical and electrical properties of lophine-based nanostructures.

DOI： 10.1021/acs.jpcc.9b01391

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© 2019 The Ceramic Society of Japan. All rights reserved. Calcium phosphates are essential compounds for the sustenance of life, since, for example, many grains that enable to convert food are necessary for use of the fertilizers made of chemically synthesized crystals. We have demonstrated two alternative dry processes for the conversion of hydroxyapatite to tricalcium phosphate by means of thermodynamically controlled heat and electronically generated heat with pulsed laser light. In addition, the conversion efficiency has been quantitatively determined from the Rietveld analysis for powder X-ray diffractionpatterns of the fired and laser-ablated samples. Both conversion processes recycled animals' bones as the source of calcium phosphate, and in the future, this could compensate for the niche area in the absence of wet process for a phosphorus containing sludge through a sewage treatment.

DOI： 10.2109/jcersj2.18190

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Society of Japan  

We prepared aqueous nanoparticle colloids of benzothiadiazole doped with diarylethene derivatives, which showed ON/OFF fluorescence photoswitching with a giant modulation of the fluorescence intensity at low density of photocolored closedform isomer of the diarylethene. The fluorescence intensity decreased nonlinearly with the photoconversion of the isomer from open-form to closed-form. The fluorescence quenching behavior was unrelated to the concentration of composed diarylethene chromophore (535mol%) in the nanoparticles.

DOI： 10.1246/cl.170973

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The excited-state dynamics of pyrene incorporated into poly(substituted methylene)s is investigated by picosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved near-IR absorption spectroscopy in the 900-1400 nm region. The pyrene rings in poly (substituted methylene)s are photoexcited to the monomer excited state immediately after UV irradiation, followed by prompt excimer formation with time constants of a few picoseconds to a few hundred picoseconds. The excimer formation in poly(substituted methylene)s proceeds with much shorter time constants than that in pyrene-incorporated polyacrylates, vinyl polymer counterparts with the same side-chain structures, indicating the presence of stronger electronic interaction between the pyrene rings in poly(substituted methylene)s. The effects of every methylene substitution hold when each pyrene ring is connected to the polymer backbone with a monomethylene linker, while the effects are observed only weakly when a tetramethylene linker is employed. The results demonstrate the effectiveness of every methylene substitution in the prompt excimer formation of pyrene connected to the polymer backbone either directly or with the monomethylene linker.

DOI： 10.1021/acs.macromol.8b01060

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© 2018 The Royal Society of Chemistry and Owner Societies. Reprecipitation of pyrene (Py) in the glassy solution of methylcyclohexane and isopentane at 77 K was observed by the repetitive irradiation of nanosecond (ns) laser pulses at 355 nm. The dynamics and mechanism of this reprecipitation were investigated by means of time-resolved fluorescence and absorption spectroscopies. Although only the fluorescence of the Py monomer was observed before the ns laser irradiation, fluorescence of the excimer was observed during the initial one-shot laser irradiation. From the time-resolved fluorescence measurements, it was revealed that the appearance of the excimer was due to the transient melting of the glassy medium by the local temperature increase around Py, which was induced by the iterative reabsorption of the laser light by the S1 state. The time period of melting for allowing the translational diffusion of Py was limited in the time region ≤ ca. 10 ns. With an increase in laser exposure, the fluorescence intensity of the excimer increased concomitantly with the appearance and increase of the amount of Py dimer, which was also confirmed by steady-state absorption spectroscopy. Time-resolved fluorescence spectrum recorded by only the one-shot laser exposure did not show dimer emission. This suggested that the formation of the dimer was through the excimer produced by transient melting; its dissociation into monomers was prohibited in the highly viscous environment. Upon further increase in laser exposure (several 1000 shots), solidified Py was observed due to crystal formation/aggregation with the dimers as the nucleation species.

DOI： 10.1039/c8pp00047f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

Naphthalocyanine nanoparticles were prepared by laser ablation in liquid using second-harmonics of nanosecond Nd:YAG laser as an excitation light sauce at various laser fluence, and the properties of naphthalocyanine nanoparticles, such as shape, size, zeta potential, chemical structure and optical absorption were examined. The scanning electron microscopy (SEM) and dynamic light scattering (DLS) measurements showed that the particle size of the nanoparticles could be controlled by the laser fluence. The IR spectra of the nanoparticles indicated the formation of carboxylate anion species at laser fluences above 100 mJ/cm2, which will result the zeta potential of the nanoparticles depending on the laser fluence. We also examined the potential application to contrast agents for photoacoustic, and confirmed that the naphthalocyanine nanoparticles generated a strong photoacoustic signal.

DOI： 10.7567/JJAP.57.035001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry  

DOI： 10.1039/c8pp90021c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Off-resonant excitation of the closed-ring isomer of a photo chromic diarylethene derivative at 730 nm induced the efficient cycloreversion reaction with a yield of similar to 20%, while the reaction yield was only 2% under one photon excitation at 365 nm. Excitation wavelength dependence of the one photon cycloreversion reaction yield under steady-state irradiation in a wide wavelength range showed that the specific electronic state leading to the large cycloreversion reaction yield, which is originally forbidden in the optical transition but partially allowed owing to the low symmetry of the molecule, is spectrally overlapped with the electronic state accessible by the allowed one photon optical transition in the UV region. Femtosecond transient absorption spectroscopy also revealed that the off-resonant two-photon excitation preferentially pumped the molecule into the specific state, leading to the 10-fold enhancement of the cycloreversion reaction.

DOI： 10.1021/acs.jpclett.7b01388

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

In the present chapter, we introduce the multiphoton-gated photochromie reactions in diarylethene and fulgide derivatives induced by picosecond pulsed laser excitation. Mechanisms of these nonlinear reactions are discussed on the basis of the detailed experimental results under various excitation conditions. In addition, one-color reversible control of photochromic reactions through nonresonant two-and three-photon absorption processes under near-IR femtosecond laser pulsed irradiation is presented as another example of the laser-induced switching of the photochemical reactions.

DOI： 10.1007/978-4-431-56544-4_11

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Language：Japanese   Publisher：日揮・実吉奨学会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Solvent polarity dependence of photochromic reactions such as cyclization and cycloreversion of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene, was investigated by steady-state spectroscopic and femtosecond laser photolysis methods. For the cyclization reaction, it was revealed that the quantum yield decreased with an increase in solvent polarities, mainly due to the decrease in the fraction of the conformer with C-2 symmetry favorable for the cyclization. This result indicated that the branching ratio for the cyclization and the deactivation to the open-ring isomer at the conical intersection was almost independent of the solvent polarity. On the other hand, it was found for the cycloreversion process that the closed-ring isomer in the S-1 state rapidly deactivated into the ground state in competition with the activated process leading to the conical intersection providing a pathway toward both open- and closed-ring minima in the ground state. The cycloreversion reaction quantum yield also decreasing with an increase in the solvent polarity was attributed to larger increase of the direct deactivation into the ground state from the excited state minimum of the closed-ring isomer.

DOI： 10.1021/acs.jpcc.5b08504

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：光化学協会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Red fluorescence lamellae in prismatic layers of Pinctada vulgaris shell were investigated. SEM-EDS, XRD, and TG-DTA were utilized to characterize prismatic layers. We found that prismatic layers are calcitic prismatic (CP) layers with rich organic substances. Excitation spectrum for red fluorescence determined by a spectrophotometer indicates that the fluorescent matter in the organic substances is porphyrin compound derivatives. By using a fluorescence microspectroscope, the cross section of CP layers shows red fluorescence forming lamellar pattern. The lamellar pattern consists of red and black parallel zones with a modulation of emission intensity. Elemental mapping show a correlation of the fluorescence intensity decay with sulphur-rich zones occupying the CP layers in the black zones. (C)2014 Optical Society of America

DOI： 10.1364/OME.4.001813

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Three 1,2-bis(2-alkyl-1-benzothiophene-3-yl)perhydrocyclopentenes with different alkyl chain lengths (methyl, ethyl, and propyl) at the reactive carbons were synthesized, and their photophysical properties were compared with those of 1,2-bis(2-alkyl-1-benzothiophene-3-yl)perfluorocyclopentenes. The structures of the perhydrocyclopentenes were analyzed by X-ray crystallography, and their cyclization/cycloreversion reaction and fluorescence quantum yields, and fluorescence lifetimes were measured by steady-state spectroscopy and the time-correlated single photon counting method, respectively. From these results, we found the following three differences between perhydrocyclopentenes and perfluorocyclopentenes. (1) For the closed-ring isomers, the absorption bands of the perhydrocyclopentenes (around 450 nm) shifted to a shorter wavelength than those of the perfluorocyclopentenes (around 530 nm) because of the acceptor nature of the perfluorocyclopentene moiety. (2) The cyclization/cycloreversion quantum yields of the perhydrocyclopentenes were slightly larger than those of the perfluorocyclopentenes in hexane. (3) Interestingly, the fluorescence of both the open- and closed-ring isomers was observed only for the perhydrocyclopentenes, and the lifetimes of the closed-ring isomers were estimated to be <30 ps. The fluorescence of the closed-ring isomers of the perhydrocyclopentenes was mainly due to the suppression of nonradiative deactivation from the excited state directly to the ground state compared with the perfluorocyclopentenes. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2014.04.007

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Excited state dynamics of biphenyl-bridged mesoporous organosilica (Bp-PMO) film was investigated by femtosecond transient absorption and dichroism measurements at various excitation intensities. Under the excitation condition with low intensity (ca. 0.1 mu J/pulse), the relaxation from the excited Franck-Condon state with skewed structure of the two phenyl rings to the preplanar state occurred with a time constant of 550 fs, followed by the excimer formation with two time constants of 9.0 and 140 ps. Under higher excitation condition with 1.0 mu J/pulse, very rapid excimer formation within 500 fs was observed. From the analysis of the transient absorption spectra, it was revealed that the cooperative geometrical relaxation from skewed to planar structures, in addition to the energy migration, led to the rapid excimer formation under the high excitation condition. By integrating these results with the fluorescence dynamics, the photoprimary processes in Bp-PMO, such as energy migration, annihilation, and excimer formation, were discussed.

DOI： 10.1021/jp502734u

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Pd-mediated polymerization of 1-pyrenylmethyl diazoacetates affords poly(1-pyrenylmethoxycarbonylmethylene) (poly4′), whose CC main chain is tightly surrounded by pyrene groups. The intensity ratio of excimer emission to monomer emission (IE/I M) of poly4′ was more than 20 times higher than that of its vinyl polymer counterpart of poly(1-pyrenylmethyl methacrylate) (polyPyrMA), clearly demonstrating much higher efficiency for excimer formation in poly4′, because of the tight arrangement of the pyrene groups around the main chain. Copyright © 2012 Wiley Periodicals, Inc.

DOI： 10.1002/pola.26480

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The photochemistry of fac-[Re(bpy)(CO)3Cl] (1?a; bpy=2,2'-bipyridine) initiated by irradiation using <330 nm light has been investigated. Isomerization proceeded in THF to give the corresponding mer-isomer 1?b. However, in the presence of a small amount of MeCN, the main product was the CO-ligand-substituted complex (OC-6-24)-[Re(bpy)(CO)2Cl(MeCN)] (2?c; bpy=2,2'-bipyridine). In MeCN, two isomers, 2?c and its (OC-6-34) form (2?a), were produced. Only 2?c thermally isomerized to produce the (OC-6-44) form 2?b. A detailed investigation led to the conclusion that both 1?b and 2?c are produced by a dissociative mechanism, whereas 2?a forms by an associative mechanism. A comparison of the ultrafast transient UV-visible absorption, emission, and IR spectra of 1?a acquired by excitation using higher-energy light (e.g., 270 nm) and lower-energy light (e.g., 400 nm) gave detailed information about the excited states, intermediates, and kinetics of the photochemical reactions and photophysical processes of 1?a. Irradiation of 1?a using the higher-energy light resulted in the generation of the higher singlet excited state with t=25 fs, from which intersystem crossing proceeded to give the higher triplet state (3HES(1)). In THF, 3HES(1) was competitively converted to both the triplet ligand field (3LF) and metal-to-ligand charge transfer (3MLCT) with lifetimes of 200 fs, in which the former is a reactive state that converts to [Re(bpy)(CO)2Cl(thf)]+ (1?c) within 10 ps by means of a dissociative mechanism. Re-coordination of CO to 1?c gives both 1?a and 1?b. In MeCN, irradiation of 1?a by using high-energy light gives the coordinatively unsaturated complex, which rapidly converted to 2?c. A seven-coordinate complex is also produced within several hundred femtoseconds, which is converted to 2?a within several hundred picoseconds.

DOI： 10.1002/chem.201202734

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Femtosecond transient absorption dynamics of C-60 nanoparticles in pure water revealed a strong quenching of the singlet excited state, independent of the excitation light intensity on a 10-ps time scale, and an extremely low yield of the triplet state of C-60 nanoparticles upon photoexcitation.

DOI： 10.1246/cl.2012.1104

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DOI： 10.1039/c2pp25078k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGERNATURE  

The sulfone derivatives of 1,2-bis(2-alkyl-6-phenyl-1-benzothiophen-3-yl)perfluorocyclopentene having various short alkyl chain substituents at reactive carbons were prepared and the effect of alkyl substitution on the fluorescence property of the closed-ring isomers was studied. Upon irradiation with ultraviolet (UV) light the derivatives exhibit a brilliant green fluorescence under irradiation with visible (> 400 nm) light, while the fluorescence disappears upon irradiation with visible (> 400 nm) light alone. The fluorescence quantum yield of the methyl substituted derivative (1b) dramatically decreases from 0.84 to 0.15 when the solvent is changed from hexane to acetonitrile, while the changes of ethyl, n-propyl and n-butyl substituted derivatives (2b)-(4b) are moderate. The quantum yields of (2b)-(4b) are kept to values close to 0.7 even in polar acetonitrile. The fluorescence lifetime measurement revealed that efficient non-radiative decay processes took place in (1b) in polar solvent, while their contribution to the deactivation was not so large in (2b)-(4b). The neighboring short alkyl chains at the connecting carbons are considered to defend the sulfone units against the attack of polar solvent molecules and weaken the solvent polarity effect.

DOI： 10.1039/c2pp25078k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Cycloreversion processes of a 1,2-bis(thiazolyl) perfluorocyclopentene photochromic diarylethene 1 with extremely low reaction yield under steady state irradiation in chloroform solution (1.3 x 10(-3)) was investigated by means of picosecond and femtosecond laser photolysis methods. The cycloreversion reaction was drastically enhanced by more than two orders of magnitude (ca. x400) by a picosecond 532 nm laser excitation in comparison with a steady state irradiation. From time-resolved transient absorption measurements, double pulse experiments, and excitation intensity dependence of the transient absorbance and the reaction efficiency, this enhancement was attributed to a stepwise two-photon absorption process leading to high excited state. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2011.12.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Primary processes of photoinduced electron transfer dynamics in a poly(N-vinylcarbazole) solid film doped with electron acceptors were investigated by means of transient absorption spectroscopy in femtosecond to microsecond time region as well as dichroism measurements. Picosecond transient dichroism measurement revealed that the rate constant of the hole shift reaction was independent of the temperature in the range between 10 and 295 K. The femtosecond transient absorption spectroscopy in the NIR wavelength region showed that the delocalization of the cationic states in sub-ps to several ps time region occurred immediately after the charge separation even at 10 K. These results indicated that the rapid delocalization of the cationic states, probably due to the small fluctuation, took an important role in the large rate constant of the hole shift reaction in PVCz solid film. In mu s time region, weak temperature dependence was observed for the dynamic behaviors. This temperature dependence was attributed to the trapping/detrapping and the charge recombination processes, which were temperature dependent. The analysis including these rate constants and the temperature independent hole shift reaction rate constant could reproduce the experimental results in the temperature range of 10-295 K. of which results also supported the temperature independence of the hole shift reaction in PVCz solid film. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2012.01.001

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Temperature dependencies of cyclization and cycloreversion processes of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), were investigated by steady-state spectroscopy and femtosecond laser photolysis methods. Steady-state measurements revealed that the cyclization reaction quantum yield and the fraction of the conformer with C-2v symmetry favorable for the cyclization (antiparallel, AP conformer) were independent of temperature in the range of 253-343 K. These results indicated that the cyclization reaction of the AP conformer in the open-ring isomer in the excited state had no apparent temperature dependence and suggested that the fate of the excited AP conformer in the open-ring isomer, such as cyclization or deactivation to the ground state, was determined at the conical intersection. On the other hand, the cycloreversion reaction was dependent on the temperature; the reaction quantum yield increased together with a decrease in the lifetime of the excited state of the closed-ring isomer with increasing temperature. On the basis of the adiabatic energy surface for the reaction profiles, it was deduced that the rapid deactivation into the ground state took place in the S-1 state in competition with the activated pathways leading to the conical intersection where the cycloreversion occurred.

DOI： 10.1021/jp2107632

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Controlling chemical reactions within a small space is a significant issue in chemistry, and methods to induce reactions within a desired position have various potential applications. Here we demonstrate localized, efficient photopolymerization by radiation pressure. We induced a one-photon UV polymerization of liquid acrylate solutions in the optical-trapping potential of a focused near-IR (NIR) laser beam, leading to the confinement of solidification to a minute space with dimensions smaller or equal to one-fifth of the wavelength of the NIR laser. Our approach can produce solidification volumes smaller than those achievable with conventional one-photon polymerization, thus enabling the production of tiny polymeric structures that are smaller than the diffraction limit of the trapping light. This is the first demonstration of a radiation pressure effect on a photochemical reaction.

DOI： 10.1021/ja200737j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Photoswitchable or photoactivatable fluorescent dyes are potentially applicable to ultrahigh density optical, memory media as well as super-resolution fluorescence imaging when the dyes are highly fluorescent and have large absorption coefficients. Here, we report on highly fluorescent photochromic dyes, which are initially nonluminous in solution under irradiation with visible light but activated to emit green or red fluorescence upon irradiation with ultraviolet (UV) light. The dyes Sa-9a are sulfone derivatives of 1,2-bis(2-ethyl-6-phenyl(or thienyl)-1-benzothiophen-3-yl)perfluorocyclopentene. It was found that substitution of phenyl or thiophene rings at 6 and 6' positions of the benzothiophene-1,1-dioxide groups is effective to increase the fluorescence quantum yields of the closed-ring isomers over 0.7 and absorption coefficients over 4 x 10(4) M-1 cm(-1). The phenyl-substituted derivatives 5a-7a undergo photocyclization reactions to produce yellow closed-ring isomers 5b-7b, which emit brilliant green fluorescence at around 550 nm (Phi(F) = 0.87-0.88) under irradiation with 488 nm light. Any absorption intensity change of the closed-ring isomers was not observed even after 100 h storage in the dark at 80 degrees C. The closed-ring isomers slowly returned to the initial open-ring isomers upon irradiation with visible (lambda > 480 nm) light. The ring-opening quantum yields (Phi(C -> O)) were measured to be (1.6-4.0) x 10(-4). When the phenyl substituents are replaced with thiophene rings, such as compounds 8a and 9a, the absorption bands of the closed-ring isomers shift to longer than 500 nm. The closed-ring isomers exhibit brilliant red fluorescences at around 620 nm (Phi(F) = 0.61-0.78) under irradiation with 532 nm light. The ring-opening reactions are very slow (Phi(C -> O) < 1 x 10(-5)). The fluorescence lifetimes of these sulfone derivatives were measured to be around 2-3 ns, which is much longer than the value of the closed-ring isomer of 1,2-bis (2-methyl-1-benzothiophen-3-yl)perfluorocyclopentene (tau(F) = 4 and 22 ps). The closed-ring isomer 8b in 1,4-dioxane exhibits excellent fatigue resistant property under irradiation with visible light (lambda > 440 nm) superior to the stability of Rhodamine 101 in ethanol

DOI： 10.1021/ja204583e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Single-molecule fluorescence photoswitching plays an essential role in ultrahigh-density (Tbits/inch(2)) optical memories and super-high-resolution fluorescence imaging. Although several fluorescent photochromic molecules and fluorescent proteins have been applied, so far, to optical memories and super-high-resolution imaging, their performance is unsatisfactory because of the absence of "non-destructive fluorescence readout capability". Here we report on a new molecular design principle of a molecule having non-destructive readout capability. The molecule is composed of acceptor photochromic diarylethene and donor fluorescent perylenebisimide units. The fluorescence is reversibly quenched when the diarylethene unit converts between the open- and the closed-ring isomers upon irradiation with visible and UV light. The fluorescence quenching is based on an electron transfer from the donor to the acceptor units. The fluorescence photoswitching and non-destructive readout capability were demonstrated in solution (an ensemble state) and at the single-molecule level. Femtosecond time-resolved transient and fluorescent lifetime measurements confirmed that the fluorescence quenching is attributed to the intramolecular electron transfer.

DOI： 10.1021/ja110686t

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Cyclization reaction of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), in nonpolar alkane solutions with different viscosity was investigated by means of femtosecond-microsecond transient absorption spectroscopy and a time-correlated single-photon counting method. Transient absorption measurements revealed that a ring closure rapidly occurred with a time constant of 450 fs. In addition to this rapid cyclization, transient species with longer lifetimes (ca. 150 ps and ca. 1 mu s) were observed. The faster time constant of 150 ps was independent of the solvent viscosity and was assigned to the fluorescence lifetime of a conformer with molecular geometry unfavorable for the ring closure. The longer component was strongly quenched in the solution purged with O(2) and was attributed to the triplet state of the open-ring form. Steady-state measurement and nanosecond transient absorption spectroscopy revealed that the cyclization process did not occur via the triplet state of BT. These results indicate that only the rapid reaction taking place in subpicosecond time region was responsible for the cyclization process. The key factors regulating the cyclization reaction of diarylethene derivatives were discussed on the basis of the solvent viscosity dependence, by comparing the present results with those obtained for other diarylethene derivatives.

DOI： 10.1021/jp112370a

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One-color control of colorization/decolorization reactions of diarylethene molecules was attained by using nonresonant high-order multiphoton absorption processes with a near-infrared (NIR) femtosecond laser pulse at 1.28 mu m with 35 fs full width at half-maximum (fwhm). The intensity of a rather weak laser pulse (< 1 nJ/pulse) can induce the simultaneous three-photon absorption leading to the colorization, while much weaker intensity induces two-photon absorption resulting in the decolorization. The spatial patterning concomitant with higher-order multiphoton absorption processes was also demonstrated.

DOI： 10.1021/ja108992t

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Ultrafast transient absorption measurement was carried out for a blue copper protein, plastocyanin, with excitation at LMCT (597 nm) and d-d band (895 nm). Franck-Condon and Herzberg-Teller type coherent nuclear oscillations were observed. © 2010 Optical Society of America.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A fluorescent photochromic molecule, which is composed of a photochromic diarylethene (DE) and a fluorescent perylenebisimide (PBI), was synthesized and its fluorescence photoswitching was studied. The fluorescence quantum yield of the open-ring isomer is constant irrespective of solvent polarity, while that of the closed-ring isomer decreases with an increase in the dielectric constant of solvents. Femtosecond time-resolved transient and fluorescence lifetime measurements revealed that the fluorescence quenching of the closed-ring isomer is attributed to the intramolecular electron transfer from the PBI chromophore to the DE unit.

DOI： 10.1039/b9pp00131j

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Ultrafast transient absorption measurements in the femtosecond to picosecond time region were carried out for a blue copper protein, plastocyanin (Pc). To compare the dynamical profiles after photoexcitation upon the ligand-to-metal-charge-transfer (LMCT) band and the d-d transition band, the pump wavelength was set at wavelengths of 597 and 895 nm, respectively. The results were nearly identical, indicating that the transition from the LMCT to the lower ligand field (LF) states takes place in an ultrafast time regime of less than 40 fs. Subsequently, relaxation in the LF state occurs with a time constant of 90 fs and the system returns to the ground state with that of 250 fs. The longest time constant of 1.8 ps was attributed to the vibrational cooling in the ground state. Several wavepacket motions were observed, including Franck-Condon type motion at similar to 510 nm and a Herzberg-Teller type motion at 660-720 nm. Critically damped low-frequency oscillation of similar to 30 cm(-1) was also observed with both excitation wavelengths with the strongest amplitude around 600 nm. This oscillation could be due to the motion of the protein that is ballistically stimulated by ultrafast relaxation.

DOI： 10.1039/b926518j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Femtosecond measurements of the transient dichroism and near-IR time-resolved spectra revealed the ultrafast delocalization of the cationic state in poly(N-vinylcarbazole), leading to carrier photogeneration.

DOI： 10.1039/b925461g

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：The Laser Society of Japan  

Organic photochromic molecules such as diarylethene and fulgide derivatives with small ring-opening

DOI： 10.2184/lsj.38.90

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Cycloreversion processes of three photochromic diarylethene derivatives with extremely low one-photon reaction yields (5.0 x 10(-5) to 1.5 x 10(-2)) were investigated by means of femtosecond and picosecond laser photolysis methods. Femtosecond visible laser photolysis revealed that the excited state of the closed form in these three derivatives decayed into the ground state with 0.7-8 ps time constants and with low cycloreversion yields that were consistent with those obtained by steady-state light irradiation. On the other hand, the cycloreversion reaction was drastically enhanced by picosecond 532 nm laser excitation for all of the three derivatives. From excitation intensity effects of the reaction yield and dynamic behavior, it was found that the successive two-photon absorption process leading to higher excited states opened an efficient cycloreversion channel, with reaction yields of 0.3 0.5. These results are discussed from the viewpoint of the one-photon inerasable but two-photon erasable photochromic system.

DOI： 10.1039/b9pp00116f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The temperature dependence of the fluorescence behaviors of 9,9'-bianthryl (BA) in the charge-transferred (CT) state in imidazolium ionic liquids (IL) was investigated by means of steady-state as well as time-resolved detections. At ambient and higher temperatures, the emission peak of BA in ILs shifted to longer wavelengths with decreasing temperature, which is a phenomenon commonly observed in normal polar solvents. On the other hand, the emission peak shifted toward shorter wavelengths with decreasing temperature below ca. 290 K. Time-resolved fluorescence (TRF) spectroscopy was carried out to investigate the dynamic Stokes shift, i.e., the time-dependent red-shift of the fluorescence peak. In highly viscous ILs, the time constant of the dynamic Stokes shift becomes comparable or longer than the lifetime of the CT state. In such a case, the ground state of BA is recovered before the completion of the solvation process. It is concluded that the origin of the blue-shifted emission at lower temperatures is due to the fluorescence from the unrelaxed CT state. It is confirmed that the charge separation process of BA in ILs occurs prior to the nanosecond fluorescence red-shift due to the slow solvation process in the CT state in the temperature range we have studied.

DOI： 10.1021/jp9020454

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Single-molecule tracking (SMT) was applied to the evaluation of a microscopic heterogeneous structure by observing the diffusivity of guest molecules in phenyl-bridged periodic mesoporous organosilica films with one-dimensional (ID) nanoscale channels filled with template surfactant micelles. SMT clearly visualized the trajectories of individual fluorescence dyes, N,N'-dipropyl-1,6,7,12-tetrakis(4-tert-butylphenoxy)-3,4,:9,10-perylenetetracarboxdiimide (BP-PDI) and N-(2,6-diisopropylphenyl)-N'-(n-octyl)-terrylene-3,4:11,12-tetracarboxidiimide (TDI), encapsulated in the channels of the mesoporous material. The ID trajectory indicated successful formation of bundled channel structures and encapsulation of the guest molecules into the channels. The encapsulation ratio of the guest dyes was strongly dependent on template surfactants. The difference was discussed in terms of the affinity between the guest molecules and surfactants. Statistical analysis for the diffusion of the guest molecules also revealed that diffusion coefficient in the channels was strongly dependent on the guest molecules and surfactants. The validity and applicability of the present approach for elucidation of a microscopic structure was discussed on the basis of the comparison between the trajectories of BP-PDI and TDI in the same sample.

DOI： 10.1021/jp902219d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The photodissociation dynamics of a hexaarylbiimidazole (HABI) derivative with two pyrenyl groups was investigated by time-resolved transient absorption spectroscopy and fluorescence measurements. Transient absorption spectroscopy revealed that photodissociation took place in the wide time region of <100 fs to 10 ns. On the other hand, fluorescence time profiles showed the dynamic red shift in the time region <100 ps. The apparent dispersive photodissociation process was attributed to the increase in the interaction between the pyrenyl moiety in the excited state and the other moiety in the ground state, resulting in the gradual increase of the activation energy for the crossing between the attractive potential surface of an excited pyrenyl unit and the repulsive potential surface.

DOI： 10.1021/ja809195s

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Cycloreversion processes of three photochromic fulgide derivatives in toluene solution were investigated by means of picosecond and femtosecond laser photolysis methods. Femtosecond laser irradiation revealed that the cycloreversion processes upon visible one-photon excitation took place within a few ps in these three derivatives. On the other hand, drastic enhancements of the reaction yield were observed under picosecond laser exposure. Excitation intensity effect of the reaction yield and dynamic behaviors revealed that the successive two-photon absorption process leading to higher excited states opened the efficient cycloreversion channel in the three derivatives. The reaction yields in higher excited states were found to be quite large in these three systems, 0.35-0.55, while those in the S(1) state were 0.048-0.21. The correlation of the reaction yield in the S(1) state with that in S(n) states suggest the character of the electronic states connected by the optical absorption plays an important role in the control of the cycloreversion reaction.

DOI： 10.1039/b900999j

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A cycloreversion reaction of a photochromic diarylethene derivative, 1-(2-methyl-3-benzothienyl)-2-(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene, with asymmetrical structure, in n-hexane solution, was investigated by means of picosecond and femtosecond laser spectroscopic methods. Femtosecond laser Spectroscopy revealed that the excited State (SI) of the closed form with a lifetime of 1,3 ps undergoies the cycloreversion reaction in competition with the internal conversion and the apparent reaction yield was independent of the excitation intensity. On the other hand, picosecond laser excitation A 532 run led to the drastic enhancement of the cycloreversion reaction yield by a successive two-photon absorption process via the S, state, leading, to hi-her excited states with a large cycloreversion yield of 0.60 +/- 0.1. For the multiphoton-enhanced cycloreversion reaction, we reported that the efficient cycloreversion reaction of a diarylethene derivative with C(2v) symmetry could occur by stepwise, visible two-photon excitation but did not take place by UV one-photon absorption to a higher excited State. Ill the present asymmetrical system, both UV one-photon land visible two-photon absorption opened the efficient cycloreversion reaction. Similarities and differences of the reaction profiles ill higher excited states between diarylethene derivatives with symmetrical and asymmetrical structures are discussed front the viewpoint of the selection rule of optical transition id its dependence oil molecular structures.

DOI： 10.1039/b818591c

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A decalin gel consisting of a 3,3'-bis[{(octylamino)carbonyl}-propoxy] azobenzene derivative with H-aggregation showed a photon-density dependent E-Z isomerization, indicating the cooperating isomerization of each module.

DOI： 10.1039/b908303k

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J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Excited state dynamics of 9,9'-bianthryl (BA) in 1-butyl-3-methylimidazolium ionic liquids with three different types of anions was investigated by means of femtosecond to nanosecond transient absorption (TA) spectroscopy and time-resolved fluorescence (TRF) measurements. TA spectroscopy revealed that charge transfer (CT) occurred multiexponentially in the time scale of hundreds of picoseconds while TRF measurement revealed that red-shift of the BA fluorescence peak extended into the nanosecond regime. It is concluded that an energy relaxation process slower than the CT reaction, which could be the solvation dynamics in the product state, is observed.

DOI： 10.1021/jp712142x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Cyclization and cycloreversion reactions of a photochromic diarylethene derivative, bis(2-methyl-5-phenylthiophen-3-yl)perfluorocyclopentene, in crystalline phase were investigated by means of picosecond laser spectroscopy. Rapid cyclization within a few picoseconds, as comparable to that in solution phase, was confirmed for the colorization reaction in the crystalline phase. On the other hand, cycloreversion reaction took place with a time constant of 25 ps. In addition, nonlinear enhancement of the cycloreversion process was observed. The excitation intensity dependence of the reaction profiles and the correlation of the apparent reaction yield with the time interval of two pulses employed for the excitation clearly revealed that the successive two-photon absorption process via the S-1 state, leading to higher excited states, opened the efficient cycloreversion process. The dynamics and mechanisms of the multiphoton-gated reaction in the crystalline phase were discussed by comparing the present results with those in solution phase.

DOI： 10.1021/jp8003272

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Dynamics of the photodissociation process of a hexaarylbiimidazole derivative, 2,2'-di(ortho-chlorophenyl)-4,4',5,5'-tetraphenylbiimidazole (o-Cl-HABI), in benzene solution was investigated by means of the femtosecond-nanosecond laser spectroscopy. The time evolution of the transient absorption of the lophyl radical, the product of the photodissociation, was biphasic with the faster and the slower time constants of 80 fs and 1.9 ps, respectively. The faster time constant was ascribable to the formation of the lophyl radical through the bond fission after the excitation, and the slower time constant may be attributed to the conformational change and/or vibrational cooling of nascent radicals. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.09.081

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

Cycloreversion (ring-opening) process of a photochromic diarylethene derivative in PMMA polymer solid film was investigated by means of picosecond laser photolysis. As was observed in our previous work in solution phase, the drastic enhancement of the cycloreversion reaction yield was observed under picosecond laser exposure. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process with reaction yield of (50 +/- 10)%. These results indicate that the multiphoton-gated reaction takes place also in the polymer solid and its efficiency was almost comparable with that in solution phase. Copyright (c) 2007 John Wiley & Sons, Ltd.

DOI： 10.1002/poc.1190

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The ultrafast electron transfer occurring upon Soret excitation of three new porphyrin-ferrocene (XP-Fc) dyads has been studied by femtosecond up-conversion and pump-probe techniques. In the XP-Fc dyads (XP-Fcs) designed in this study, the ferrocene moiety is covalently bonded to the meso positions of 3,5-di-tert-butylphenyl zinc porphyrin (BPZnP-Fc), pentafluorophenyl zinc porphyrin (FPZnP-Fc), and 3,5-di-tert-butylphenyl free-base porphyrin (BPH2P-Fc). Charge separation and recombination in the XP-Fcs were confirmed by transient absorption spectra, and the lifetimes of the charge-separated states were estimated from the decay rate of the porphyrin radical anion band to be approximately 20 ps. The charge-separation rates of the XP-Fcs were found to be > 10(13) s(-1) from the S-2 state and 6.3 x 10(12) s(-1) from the S-1 state. Charge separation from the S-2 state was particularly efficient for BPZnP-Fc, whereas the main reaction pathway was from the S-1 state for BPH2P-Fc. Charge separation from the S-2 and S-1 states occurred at virtually the same rate in benzene and tetrahydrofuran and was much faster than their solvation times. Analysis of these results using semiquantum Marcus theory indicates that the magnitude of the electronic-tunneling matrix element is rather large and far outside the range of nonadiabatic approximation. The pump-probe data show the presence of vibrational coherence during the reactions, suggesting that wavepacket dynamics on the adiabatic potential energy surface might regulate the ultrafast reactions.

DOI： 10.1021/jp071546b

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Cycloreversion processes of a photochromic diarylethene derivative, bis(2-methyl-5-phenylthiophen-3-yl)perfluorocyclopentene, in crystalline phase was investigated by means of the picosecond laser spectroscopy. In addition to the cycloreversion process in the S, state with 50 ps time constant, drastic enhancement of the reaction yield was observed by the picosecond laser exposure. The excitation intensity effect of the reaction yield and dynamic behaviors revealed that successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process. The dynamics and mechanisms of the multiphoton-gated reaction in the crystal were discussed by comparing the present results with those in solutions. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.02.032

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A cycloreversion (ring-opening) process of one of the photochromic fulgide derivatives, 2-[1-(2,5-dimethyl-3-fulyl)-2-methylpropylidenel-3-isopropylidenesuccinic anhydride, was investigated by means of picosecond and femtosecond laser photolysis methods. The drastic enhancement of the reaction yield was observed by the picosecond laser irradiation. On the other hand, the cycloreversion reaction yield under femtosecond laser exposure was almost consistent with the steady-state light irradiation. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process. The multiphoton-gated reaction for photochromic compounds as diarylethene derivatives was confirmed also for a fulgide derivative. The similarities and differences of the reaction profiles in higher excited states between fulgides and diarylethenes were discussed from the viewpoints of selection rule of optical transition and its dependence on molecular structures.

DOI： 10.1021/jp0650578

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The enhancement of the cycloreversion reaction of photochromic fulgides was observed not by the femtosecond laser but by the picosecond laser exposure. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process.

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Photoinduced electron transfer (ET) and excitation energy transfer (ENT) reactions in monomer and slipped-cofacial dimer systems of a directly linked Zn porphyrin (Por)-Zn phthalocyanine (Pc) heterodyad, ZnPc-ZnPor, were investigated by means of the picosecond and femtosecond transient absorption spectroscopies. In the dimer dyad system of two heterodyads connected through the coordination bond between two imidazolyl-substituted ZnPor bearing ZnPc, ZnPc-ZnPor(D), the rapid ENT from the ZnPor to ZnPc in the subpicosecond time region was followed by photoinduced charge separation (CS) and charge recombination (CR) with time constants of 47 and 510 ps, respectively. On the other hand in the monomer dyad system, no clear charge-separated state was observed although the CS with a time constant of 200 ps and CR with <= 70 ps were estimated. These results indicated that the dimer slipped-cofacial arrangement of pair porphyrins is advantageous for the effective production of the CS state. This advantage was discussed from the viewpoint of a decrease in the reorganization energy of the dimer relative to that of the monomer system. In addition, the electrochemical measurements indicated that the strong interaction between ZnPc and ZnPor moieties also contributed to the fast CS process despite the marginal driving force for the CS process. The dimer dyad of ZnPc-ZnPor provides full advantages in efficiencies of the light harvesting and the CS state production.

DOI： 10.1021/jp062822+

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Ultrafast electron transfer in a porphyrin-ferrocene dyad in which the ferrocene moiety is directly linked at the meso-position of the porphyrin was studied using femtosecond up-conversion and pump-probe techniques. The time constant of electron transfer was similar to 110 fs both in benzene and tetrahydrofuran. Vibrational coherence of the 130-, 200-, and 250-cm(-1) modes, which were assigned to the translation and rotation of ferrocene, was observed, and was found to be phase shifted with respect to the vibrational coherence of the 330-cm(-1) mode. The relation between this behavior of vibrational modes and electron transfer is discussed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.07.082

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(ii)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization a,, well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N=5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.

DOI： 10.1002/chem.200500069

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Picosecond laser spectroscopy was applied to the direct detection of photochromic reaction processes in a network polymer film prepared by oxidation polymerization of a diarylethene derivative. Both the coloration due to the cyclization and the decoloration via the cycloreversion took place in less than 30 ps. The time constants of both photochromic reactions were almost the same as those of diarylethene monomers obtained in the solutions, indicating that the oxidation polymer film system retains a similarly high response time as in the solution phase.

DOI： 10.1039/b500516g

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Ultrafast pump-probe measurement was applied to investigate the excited state deactivation dynamics of bisimidazolyl radical, 1,4-bis-(4,5-diphenylimidazol-2-ylidene)cyclohexa-2,5-diene (BDPI-2Y). BDPI-2Y is non-fluorescent and the recovery of the ground state took place in the time scale of femtoseconds to picoseconds, indicating a direct ultrafast nonradiative decay from the excited state. Coherent intermolecular vibrations were also observed and the low-frequency mode at 150 cm(-1) and 128 cm(-1) had a phase shift of similar to pi compared to the mode at 290 cm(-1).

DOI： 10.1080/15421400590946866

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

We report coherent nuclear dynamics coupled with photoinduced electron transfer using a newly designed donor-acceptor system with a strong electronic coupling. Our results by femtosecond spectroscopy show that the ultrafast electron transfer (similar to 110 fs from S-1 and similar to 60 fs from S-2) was independent of solvent properties. Moreover, the electron transfer was accompanied by temporal phase shift of the selective porphyrin vibrational modes. The reaction coordinate for ultrafast electron transfer was shown to involve coherent intramolecular motions of the selective modes rather than stochastic solvation dynamics.

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Language：English  

DOI： 10.1080/15421400590946866

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General Education / Liberal Arts Section

General Education / Liberal Arts Section

Faculty of Engineering / Specialized Subjects

Faculty of Engineering / Specialized Subjects

Faculty of Engineering / Specialized Subjects